Watch This Space

It was quite a surprise to discover, when I looked it up, that the most

famous experiment we carried out while we were on the moon had its

begimungs way back in 19SS. At that time, high-altitude rocket

research had been going for only about ten years, mostly at White

Sands, New Mexico. Nineteen fifty-five was the date of one of the most

spectacular of those early experiments, one that involved the ejection

of sodium into the upper atmosphere.

On Earth, even on the clearest night, the sky between the stars isn't

completely dark. There's a very faint background glow, and part of it

is caused by the fluorescence of sodium atoms a hundred miles up. Since

it would take the sodium in a good many cubic miles of the upper

atmosphere to fill a single matchbox, it seemed to the early

investigators that they could make quite a fireworks display if they

used a rocket to dump a few pounds of the stuff into the ionosphere.

They were right. The sodium squirted out of a rocket above White Sands

early in 195S produced a great yellow glow in the sky which was

visible, like a kind of artificial moonlight, for over an hour, before

the atoms dispersed. This experiment wasn't done for fun (though it

was fun) but for a serious scientific purpose. Instruments trained on

this glow were able to gather new knowledge about the upper air

knowledge that went into the stockpile of information without which

space flight would never have been possible.

When they got to the moon, the Americans decided that it would be a

good idea to repeat the experiment there, on a much larger scale. A

few hundred kilograms of sodium fired up from the surface would produce

a display that would be visible from Earth, with a good pair of field

glasses, as it fluoresced its way up through the lunar atmosphere.

(Some people, by the way, still don't realize that the moon has an

atmosphere. It's about a million times too thin to be breathable, but

if you have the right instruments you can detect it. As a meteor

shield, it's first-rate, for though it may be tenuous it's hundreds of

miles deep.)

Everyone had been talking about the experiment for days. The sodium

bomb had arrived from Earth in the last supply rocket, and a-very

impressive piece of equipment it looked. Its operation was extremely

simple; when ignited, an incendiary charge vaporised the sodium until a

high pressure was built up, then a diaphragm burst and the stuff was

squirted up into the sky through a specially shaped nozzle. It would

be shot off soon after nightfall, and when the cloud of sodium rose out

of the moon's shadow into direct sunlight it would start to glow with

tremendous brilliance.

Nightfall, on the moon, is one of the most awe-inspiring sights in the

whole of nature, made doubly so because as you watch the sun's flaming

disk creep so slowly below the mountains you know that it will be

fourteen days before you see it again. But it does not bring darkness

at least, not on this side of the moon. There is always the Earth,

hanging motionless in the sky, the one heavenly body that neither rises

nor sets. The light pouring back from her clouds and seas floods the

lunar landscape with a soft, blue-green radiance, so that it is often

easier to find your way around at night than under the fierce glare of

the sun.

Even those who were not supposed to be on duty had come out to watch

the experiment. The sodium bomb had been placed at the middle of the

big triangle formed by the three ships, and stood upright with its

nozzles pointing at the stars. Dr.

Anderson, the astronomer of the American team, was testing the firing

circuits, but everyone else was at a respectful distance. The bomb

looked perfectly capable of living up to its name, though it was really

about as dangerous as a soda-water siphon.

All the optical equipment of the three expeditions seemed to have been

gathered together to record the performance. Telescopes,

spectroscopes, motion-picture cameras, and everything else one could

think of were lined up ready for action. And this, I knew, was nothing

compared with the battery that must be zeroed on us from Earth. Every

amateur astronomer who could see the moon tonight would be standing by

in his back garden, listening to the radio commentary that told him of

the progress of the experiment. I glanced up at the gleaming planet

that dominated the sky above me; the land areas seemed to be fairly

free from cloud, so the folks at home should have a good view. That

seemed only fair; after all, they were footing the bill.

There were still fifteen minutes to go. Not for the first time, I

wished there was a reliable way of smoking a cigarette inside a space

suit without getting the helmet so badly fogged that you couldn't see.

Our scientists had solved so many much more difficult problems; it

seemed a pity that they couldn't do something about that one.

To pass the time for this was an experiment where I had nothing to do I

switched on my suit radio and listened to Dave Bolton, who was making a

very good job of the commentary. Dave was our chief navigator, and a

brilliant mathematician. He also had a glib tongue and a picturesque

turn of speech, and sometimes his recordings had to be censored by

the

BBC.

There was nothing they could do about this one, however, for it was

going out live from the relay stations on Earth.

Dave had finished a brief and lucid explanation of the purpose of the

experiment, describing how the cloud of glowing sodium would enable us

to analyze the lunar atmosphere as it rose through it at approximately

a thousand miles an hour.

"However," he went on to tell the waiting millions on Earth, "let's

make one point clear. Even when the bomb has gone off, you won't see a

darn thing for ten minutes and neither will we. The sodium cloud will

be completely invisible while it's rising up through the darkness of

the moon's shadow.

Then, quite suddenly, it will flash into brilliance as it enters the

sun's rays, which are streaming past over our heads right now as we

stare up into space. No one is guise sure how bright it will be, but

it's a pretty safe guess that you'll be able to see it in any telescope

bigger than a two-inch. So it should just be within the range of a

good pair of binoculars."

He had to keep this sort of thing up for another ten minutes, and it

was a marvel to me how he managed to do it. Then the great moment

came, and Anderson closed the firing circuit. The bomb started to

cook, building up pressure inside as the sodium volatilised. After

thirty seconds, there was a sudden puff of smoke from the long, slender

nozzle pointing up at the sky. And then we had to wait for another ten

minutes while the invisible cloud rose to the stars. After all this

build-up, I told myself, the result had better be good.

The seconds and minutes ebbed away. Then a sudden yellow glow began to

spread across the sky, like a vast and unwavering aurora that became

brighter even as we watched. It was as if an artist was sprawling

strokes across the stars with a flame-filled brush. And as I stared at

those strokes, I suddenly realised that someone had brought off the

greatest advertising coup in history. For the strokes formed letters,

and the letters formed two words the name of a certain soft drink too

well known to need any further publicity from me.

How had it been done? The first answer was obvious. Someone had

placed a suitably cut stencil in the nozzle of the sodium bomb, so that

the stream of escaping vapor had shaped itself to the words. Since

there was nothing to distort it, the pattern had kept its shape during

its invisible ascent to the stars. I had seen skywriting on Earth, but

this was something on a far larger scale.

Whatever I thought of them, I couldn't help admiring the ingenuity of

the men who had perpetrated the scheme. The O's and A's had given them

a bit of trouble, but the C's and L's were perfect.

After the initial shock, I am glad to say that the scientific program

proceeded as planned. I wish I could remember how Dave Bolton rose to

the occasion in his commentary; it must have been a strain even for his

quick wits. By this time, of course, half the Earth could see what he

was describing. The next morning, every newspaper on the planet

carried that famous photo of the crescent moon with the luminous slogan

painted across its darkened sector.

The letters were visible, before they finally dispersed into space, for

over an hour. By that time the words were almost a thousand miles

long, and were beginning to get blurred. But they were still readable

until they at last faded from sight in the ultimate vacuum between the

planets.

Then the real fireworks began. Commander Vandenburg was absolutely

furious, and promptly started to grill all his men. However, it was

soon clear that the saboteur if you could call him that had been back

on Earth. The bomb had been prepared there and shipped ready for

immediate use. It did not take long to find, and fire, the engineer

who had carried out the substitution. He couldn't have cared less,

since his financial needs had been taken care of for a good many years

to come.

As for the experiment itself, it was completely successful from the

scientific point of view; all the recording instruments worked

perfectly as they analyzed the light from the unexpectedly shaped

cloud. But we never let the Americans live it down, and I am afraid

poor Captain Vandenburg was the one who suffered most. Before he came

to the moon he was a confirmed teetotaler, and much of his refreshment

came from a certain wasp-wasted bottle. But now, as a matter of

principle, he can only drink beer and he hates the stuff.